Hi all. A family member asked me if i can make them a few small 3d rocking char ornaments similar to this. I think the one in the photo is done with a laser but i dont have one so im hoping to do it on my cnc. My thought process is designing 4 peices, 2 sides, back and seat that can fit together. Im just not sure how to approach the joinery element. Any advice on how i can go about accomplishing this?
Mortise and full thickness tenons. See:
Looks like straight forward mortise and tenon. The seat and back each have four “tabs” projecting to the sides (the tenons). The sides have “slots” cut into them (the mortises) to accept the tenons. Cut the mortises very slightly larger than the tenons, how much depends on the overall size and, to some extent, the type of wood.
Finish up the mortise corners with a small bit to roughly square them off or sand/file the tenons to fit into the rounded corners of the mortise.
Also, make the tenons very slightly longer than the thickness of the sides so they will sand flush.
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The biggest problem is that the CNC can’t make square corners for the joint cut-outs. You can either clean them up by hand, or create ‘dog-bone’ corners. This basically over-cuts the rectangle so that the entire rectangle is cut (plus a bit more):
CC can add these to rectangles for you:
If you do this, you want to set the radius of the dog-bone to be slightly greater than the radius of your tool. So, if you are using a 1/8" bit (diameter 0.125", radius 0.0625"), set the dog-bone radius to 0.065" or 0.07".
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A laser has an extremely thin kerf. That would be difficult to do on such thin stock with a router.
For an ornament, I’d think glue would be enough.
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Thanks for eveyones help with this, the dogbone slots worked out really well. One question i do have: for these i just manually placed the mortise and tenon and and lined things up using carbide create. My question is , Once you know how many and the dimensions of the mortise and tenons, is there a fairly simple way to accurately create and line things up correctly? Im thinking this could be very useful for finger joints as well.
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When I want things to line up, I model them in 3D.
Alibre Atom3D should work well for this:
(still working through tutorials trying to figure it out)
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